Chairs of many different designs are currently available. In many chair designs, the most common seat configuration in one in which the seat Is substantially flat and disposed with a slight backward tilt. This configuration induces an undesirable seated posture and creates a transverse pressure ridge against the underside of the user's legs.
In improved chair designs, the seat is provided with a forward tilt to encourage a more erect posture and the correct lordosis of the lower back. When using such chair designs, the knees are lower than the hips and the normal curve of the spine is encouraged. As the tilt of the chair seat increases however, means are required to be provided to prevent a person seated on the chair from sliding off the seat.
The use of knee rests is common for such purposes, however knee rests create certain difficulties as considerable pressure Is applied to the knees which can thus be aggravated. Furthermore, chairs of this design reduce the freedom of movement of the person's posture and additionally the chairs themselves are more cumbersome
Various seat contours have also been proposed to prevent sliding from a tilted seat. Most however have as their principal object the restraint of sliding and thus are not adapted for comfortable effective seating. For example, one earlier proposal utilises a seat contour formed with a transverse V-shaped recess which would not be particularly comfortable in use. Others provide a forward-elevating central ridge which would also be uncomfortable for many users.
Furthermore, these arrangements do not maintain a desired posture wherein the skull, neck, lower backbone and Ischial Tuberosities of the pelvis are substantially maintained in vertical alignment while the user's weight is transferred to a relatively flat horizontal surface.
Also, in many prior proposals tilting seats are considered desirable. In this respect it is believed that small amplitude tilting movements of the spine stimulate nutrient secretion to the spine. However most use conventional tilting arrangements which result in the user's body being raised and lowered with the tilting action This changes the body's height in relation to the desk which is most undesirable. Thus the desired relationship between hip and knees and the desk at which the person is seated is varied with the tilting. Furthermore when in a tilted position, offset pressure must be applied to the seat in order to maintain the desired tilted attitude. This further reduces the relaxed attitude of the user's body and increases stress.
The present invention aims to alleviate one or more of the above disadvantages.